A programmable display device is an operational display device having an interface with a host controller (PLC), and having functions such as for displaying an operating condition of a device connected to the host controller and receiving from a screen an operational input for giving control instructions to the device. Generally, a programmable display device has a graphical display function, and accordingly can display an console, a switch, a display lamp and the like, so as to serve as an operating terminal in a controlling system.
A screen displayed on such a programmable display device can be created by a user, using screen creation software, according to a specification of a controlling system. In creating a screen, the user uses parts, a drawing function and the like provided by the screen creation software in a personal computer and the like, so as to create a desired screen.
The parts are images for illustrating a switch, a numeric keypad, a meter display device, a graph display device and the like, and are provided in a library form in the screen creation software so as to be combined and used in the same manner as real parts. Further, the parts are used in a manner where images for showing the parts, and assigning data for displaying dynamic changes of the images on a specified position of the screen, are combined with one another. The assigning data is stored as a portion of screen data in a memory of the programmable display device.
The created screen is transferred as the screen data to the programmable display device and stored therein. When the host controller is in operation, an output part such as the meter display device, displayed on the screen displayed on a display section of the programmable display device, changes dynamically according to a condition of a device connected to the host controller. Further, input operations performed on the screen at an input part displayed on the screen, such as a switch, is provided to the device as control instructions.
Generally, in screen creation software, in order to reflect a condition of a device on a displayed screen, or to reflect an input instruction via a part on a condition of the device, an address of a memory in a PLC for storing data of the device is assigned to the part. To perform such assigning of an address, it is necessary to determine which address is unused and available. A document disclosing a technique for determining unused addresses is Japanese Laid-Open Patent Publication 2000/47775 (Tokukai 2000-47775) (published date; Feb. 18, 2000). This document discloses a technique for displaying, by use of a figure, a memory range of a PLC and for displaying, within the memory range, by use of a figure, an address range that is referred to by the programmable display device. As a result, it is easy to determine which addresses out of the entire range of addresses are unused.
Conventional screen creation software can determine a condition of address usage as described above, but when an unused address is determined and the address is then assigned to a part, there are the following problems.
First, display of a figure (an address displaying figure) for displaying a usage condition of addresses is performed as a process different from that of assigning of an address. Therefore, it is necessary to confirm an unused address, temporarily close a screen of an address displaying figure, and then open a screen for assigning of an address. As a result, it is not possible to view the address displaying figure while performing assigning of an address, such that it is not possible to make real-time confirmation of a currently assigned address in the address displaying figure.
Next, when the address displaying figure is displayed, a process is carried out in which parts on the all screens are scanned one by one so as to confirm which address is used for which part. As a result, the more numerous the number of screens becomes, the longer it takes to display the address displaying figure.